1. Field of the Invention
The present invention relates to an apparatus for discriminating a type of document, an image of which is read by an image sensor or a scanner unit.
2. Description of the Prior Art
Comparison between an original document and a duplicate (a copy) thereof proves that deterioration occurs in the duplicate, for example, an indentation appears at an edge of a line drawing or a character, a halftone dot appears in a background color, or in a subtle color in a picture such as a portion of human skin, or a color is replaced by a color different from that of an original document. When the duplicate in which the deterioration mentioned above occurs is used as a document to be duplicated to produce a copy, i.e., when a copied document is copied, further deterioration may occur under the same process as the case of reproducing an original document.
There is proposed a method in which a process is performed for a scanned image of a document in reproducing the document, the process depending on the type of the document. According to the invention disclosed in related patent publication 1 mentioned below, for example, it is discriminated whether a document is an original document or a copied document thereof (hereinafter referred to as a “generation document”), and parameters for black character processing are changed based on the discrimination result and a process is conducted. Each of related patent publications 2 and 3 mentioned below discloses a process depending on a type of document, similarly to the related patent publication 1.
Thus, processing contents are changed depending on whether a document is an original document or a generation document, thereby ensuring that deterioration seen in an image of a duplicate can be minimized and the duplicate close to an original document can be obtained.
The related patent publications 1 to 4, which are mentioned below, disclose methods for discriminating a type of document mentioned below. According to the related patent publication 1, a document is discriminated as an original document when a plurality of pixels in a scanned image of a document cannot be reproduced in outputting the image to a sheet of paper. When one or less pixel cannot be reproduced, the document is discriminated as a generation document.
According to the method, however, when a scanned image of a document has low saturation, one or less pixel cannot be reproduced even if the document is a generation document. Therefore, the document may be determined as an original document by mistake. Additionally, when a document to be read is a colored paper or marked with a writing material, also, there is a case where improper discrimination may be made.
According to the related patent publication 2, an image having a predetermined pattern embedded is reproduced on a sheet of paper. A document is determined as a generation document when the pattern is detected from the scanned image of the document in reproduction. A document is determined as an original document when the pattern is not detected. The related patent publication 3 discloses that a predetermined pattern is embedded at reproduction, similarly to the related patent publication 2. The method in the related patent publication 3, however, is inapplicable to a case where a document to be reproduced is a duplicate output from a copier with no function of embedding the pattern. Accordingly, there is a situation where a document to be reproduced is discriminated as an original document by mistake even if the document to be reproduced is a generation document.
According to the related patent publication 4, it is discriminated whether a document is a character document, a photodocument or a halftone dot document, and correction processing is conducted, the processing being different depending on the type of the document. However, it is impossible to determine whether a document is an original document or a generation document using this method.    Related Patent Publication 1:
Japanese unexamined patent publication No. 8-130636    Related Patent Publication 2:
Japanese unexamined patent publication No. 7-307861    Related Patent Publication 3:
U.S. Pat. No. 6,091,520    Related Patent Publication 4:
Japanese unexamined patent publication No. 7-298074